Doppler measurements
Positrons that annihilate with a fast moving electron (i.e.: a core electron) will emit Doppler-shifted gamma rays. Detecting these gamma rays in coincidence can then give us information about the chemistry at the annihilation site. As positrons tend to be attracted to defects in the materials, this then gives us the ability to determine the chemical makeup at defect sites, such as voids, which may be sites for solute atoms forming clusters or precipitates, for instance.
